Radio controlled mine



Nov. 26, 1946.

J. H. HAMMOND, JR

RADIO CONTROLLED NINE Filed Sept. 26, 1942 3 Sheets-Sheet 1 EXPLOSIVE HIiF DETONATINGI CIRCUIT RAD I D TRANSMITTER RADI O R ECEIVER INVENTOR JOHN HgYS HAMMOD.,JE

III/IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Nov. 26, 1946. M D, JR 2,411,787

RADIO CONTROLLED MINE Filed Sept. 26, 1942 3 Sheets-Sheet 2 Nov. 26, 1946. H HAMMOND, JR 2,411,787

RADIO CONTROLLED MINE Filed Sept. 26, 1942 3 Sheets-Sheet 3 INVENTOR JOHN HAYS HAMMOND.,JR.

Patented Nov. 26, 1946 RADIO CONTROLLED MINE John Hays Hammond, Jr., Gloucester, Mass, assignor to Radio Corporation of America Application September 26, 1942, Serial No. 459,787

(Cl. IMP-3) 8 Claims. I

This invention relates to mines which detonate when approached by moving objects and has for an object to provide means responsive to radiant energy signals for rendering the detonating mechanism inoperative.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be partlcularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Figure 1 illustrates schematically the radio controlled mine in relation to an approaching tank;

Figure 2 shows diagrammatically the circuits employed in one type of radio transmitter on the tank; and

Figure 3 depicts diagrammatically the circuits employed in one type of radio receiver at the mine.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specific terms for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the accompanying drawings and more particularly to Figure 1 a mine ii is shown as buried in the ground. The mine ll comprises an explosive charge !2, a detonator l3 for exploding said charge, a detonating circuit M and a radio receiver IS. The detonating circuit l4 may be of any well known construction, such for example, as a magnetically operated device which is connected to a relay l6 and which is operated by the approach of a metallic object such as a tank ll. The relay I6 is in circuit with the detonator l3, a battery I8 and relay IS the contacts of which are normally closed but are arranged to be opened by the radio receiver l5.

Transmitter In the tank I! is mounted a transmitter 25 which comprises three tone generators 22, 23 and 24, a modulator 25, a master oscillator 26, a buffer doubler 2'1 and a power amplifier 28. The tone generators 22, 23 and 24 are of well known construction and generate three distinct frequencies which for example may be of 600, 800 and 1100 cycles respectively. The difference between any two of the frequencies preferably is not the same as the difference between any other two frequencies, and they are preferably within a single octave. If desired these frequencies may be super or subaudible.

The three tone generators 22, 23 and 24 each comprise a triode tube the cathode of which is connected to ground thru a cathode resistor and a condenser it. The plate circuit of the tube 75 includes an oscillatory circuit 11 with a feed back E8 to the grid. From taps on the feed back coils 28 energy is fed into the combining circuit thru mixing resistors '59. Plate feed resistors are provided and are adjusted so that approximately the same voltage to the common circuit results from the three oscillators 22, 23 and 24.

The combining circuit 25 comprises a triode 8! with cathode biased by means of the resistor-condenser circuit 32. The grid of the tube 8| is connected to the contact of a switch 83, the blade of which is ground. The plate circuit'of the tube 53! is coupled to the grids of two modulator tubes 34 and 35 by means of a band pass filter 86 which transmits the three frequencies produced by the three tone generators 22, 23 and 24. The earth odes of the tubes 84 and 85 are biased positively with respect to ground by the resistor 81. The plates of the tubes 84 and 85 are connected to the primary winding of a modulation transformer 88 the center tap of which is polarized positively with respect to ground by plate battery 89.

The frequency of radiooscillation of the cscil lator 25 is determined by a piezo electric crystal the connected between the control grid of a pehtode 90 and ground and shunted by radio frequency choke @l and resistor 92. The cathode of tube 90 is biased positively to ground by cathode resistor and condenser 93 and is also connected to the third grid. The positive end of a battery 34 is connected to the second grid of the tube 90 and thru a circuit 35, tuned to the crystal frequency, to the plate of tube 90. The plate is connected to the control grid by condenser 96, which may be represented by the internal capacity of the tube 96.

g A tap on the coil of the tune-d circuit 95 is connected to the control grid of a doubler tube 91 by coupling condenser 98. The control grid of tube 91 is conductively connected to ground thru choke 99 and resistor Hill, which is shunted by condenser ml. The cathode of tube 91 is connected to the third grid and thru a cathode resistor and condenser M2 to ground. The positive side of a plate supply battery I03 is con-= nected to the second grid of the tube 91 and thru 3 a circuit I04, tuned to double the crystal frequency, to the plate of the tube 81.

A tap on the coil of the tuned circuit I54 is connected to the control grid of a pentode I85 by coupling condenser I85. The control grid of the tube I is conductively connected to ground thru a choke I81 and resistor I 88, which is shunted by condenser I88. The cathode of tube I85 is connected to the third grid and thru a cathode resistor and condenser III to ground. The second grid of tube I85 is connected thru a resistor II 2 to the positive side of a plate battery II8 the negative side of which is grounded. The second grid is also connected thru a resistor II4 to the contact of switch III! the blade of which is connected to ground. The switches 88 and Ill may be interconnected so as to be operated in unison.

The positive side of the plate battery H8 is connected thru the secondary of the modulation transformer 88, radio frequency choke H5 and oscillatory circuit I I8, tuned to double the crystal frequency, to the plate of the tube I85. A radio frequency bypass condenser I I1 is connected from the positive side of battery II3 to the junction of the choke H5 and circuit I I5. The oscillatory circuit H5 is coupled to a coil II8 one end of which is grounded and the other end connected thru a loading coil H9 and tuning condenser I2I to an antenna I22.

In the operation of the transmitter depicted in Figure 2 high frequency energy will be generated by the master oscillator 28 the frequency of which will be determined and held constant by the piezo-electric crystal 88a. The frequency of this energy will be doubled by the bufler doubier 21 and will be impressed upon the power amplifier 28. With the switch IIIl closed the power amplifier 28 will be inoperative so that no energy will be radiated by the antenna I22.

The three tone generators 22, 28 and 24 each generate a diflerent frequency, which for example may be 600, 800 and 1100 cycles respectively. When the switch 88 is closed the tone generators 22, 28 and 24 do not affect the modulator 25. When the switch 88 is open, however, energy of 600, 800 and 1100 cycles is impressed upon the modulator 25, so that modulating energy is impressed upon the plate of the tube I 85. When the switch III! is opened the power amplifier 28 becomes operative and causes high frequency energy, modulated at 600, 800 and 1100 cycles, to be radiated from the antenna I22. The switches 88 and H8 may be interconnected so that the two operations occur simultaneously or switch IIII may be opened to produce radiations prior to opening switch 88 to cause modulation of the radiations.

- Receiver Referring to Figure 3 a receiver is shown for receiving the energy radiated by the antenna I22 of the transmitter. This receiver comprises a radio frequency amplifier 4| connected to an antenna-42, a detector and audio amplifier 48, a plurality of tuned circuits 44, combining and amplifying circuits 45, two rectifying and detecting circuits 48 and 41 and a relay tube circuit 48.

The antenna 42 is connected thru a condenser I8I to a tap on a radio tuning coil I82 one terminal of which is connected to the AVG line and the other to the grid of a radio amplifier tube I88. A condenser I84 is connected between the AVG line and ground and a tuning condenser I85 is connected between the control grid of tube I88 and ground. The cathode of tube I88 is con- 4 nectedtothethirdgridandtoground. The screen mid of tube I88 is connected to the positive side of a battery I'and to the negative side of a battery I81, the positive side of which is connected thru the primary circuit of a tuned transformer I88 to the plate of tube I88.

The secondary circuit of the transformer I88 is connected to the diode plate of detector amplifier tube I and to the AVG line. The cathode of the tube I is connected thru a cathode resistor and condenser I42 to ground and also thru tapped resistor I48. shunted by condenser I44, to the AVG line. The grid is connected thru condenser I45 to the tap of resistor I48 and is also connected thru a resistor I48 to ground. The plate of tube MI is connected thru three tuned circuits 53, 52 and 5i to the positive side of a battery I41 the other side of which is grounded.

The three tuned circuits 5i, 52 and 58 are tuned to the three frequencies of the three tone generators 22, 28 and 24 of the transmitter deplcted in Figure 2. These frequencies for example may be 600, 800 and 1100 cycles respectively. The tuned circuit 5| is loosely coupled to a secondary tuned circuit 54 which is tuned to 600 cycles, the tuned circuit 52 is loosely coupled to two secondary tuned circuits 55 and 55 both of which are tuned to 800 cycles and the tuned circuit 58 is loosely coupled to a secondary tuned circuit 51 which is tuned to 1100 cycles.

The tuned circuits 54 and 51 are connected thru rectifiers 58 and 58 to two tuned circuits 8i and 52 which are tuned to frequencies of 200 and 300 cycles respectively. The combining and amplifying circuits 45 comprise two amplifiers 58 and 54 the output circuits of which are. connected to the primary of a transformer-85 both the primary and secondary of which are broadly tuned to 200 to 300 cycles. The secondary of the transformer 55 is connected to the rectifying and detecting circuit 45. This circuit includes a rectifier 55 and the primary of a transformer 51 which is tuned to a frequency of cycles by means of a condenser 51a.

The secondary of the transformer 51 is tuned to 100 cycles by means of a condenser 18 and is connected to the rectifying and detecting circuit 41 which includes a rectifier 58 and a resistor 58. The rectifying circuit 41 is connected thru a time delay circuit H to the relay tube circuit 48 the output circuit of which includes the winding of the relay I8.

In the operation of the receiver shown in Figure 3, the radio signal is received by the antenna 42 and is amplified by the radiofrequency amplifier U. The amplified signal is detected and further amplified by the detector and audio amplifier 43. The output of the audio amplifier 48 is fed to the three tuned circuits 5i, 52 and 58 where the three frequencies of 600, 800 and 1100 cycles are selected by the three circuits 5 I, 52 and 58 respectfully.

Currents of 600 cycles are induced in the tuned circuit 54 as the circuits 5| and 54 are sufllciently loosely coupled so that they transmit 600 cycles and not the other two frequencies of 800 and 1100 cycles. Currents of 800 cycles are induced in the tuned circuit 55 as the circuits 52 and 55 sufiiciently loosely coupled so that they transmit 800 cycles and not the other two frequencies. The currents of 600 and 800 cycles are detected by the rectifier 58 and a current having their diilerence frequency. namely 200 cycles, is induced in the tuned circuit 8| which is tuned to this frequency. In a similar manner, currents of 800 and 1100 cycles are induced in the tuned circuits 56 and 51 respectively. These currents are detected by the rectifier 59 and a current having their difference frequency, namely 300 cycles is induced in the tuned circuit 62 which is tuned to this frequency.

The currents of 200 and 300 cycles are amplified by the amplifiers 63 and 64 respectively, and are combined in the tuned circuit which includes the primary of the transformer 65, which is sufficiently closely coupled so that the transformer as a whole transmits 200 and 300 cycles. Currents of 200 and 300 cycles are induced in the secondary of the transformer 85 and are detected by the rectifier 66 and a current having their difference frequency, namely 100 cycles, is fed to the tuned circuit which includes the primary of the transformer 61, which is tuned tothis frequency.

Current of 100 cycles is induced in the secondary of the transformer 61, is rectified by the rectifier 68 and flows thru the resistor 69 in the direction of the arrow. Under normal conditions the relay tube 48 operates with no bias on the grid so that a steady current flows thru the winding of the relay l9 keeping it energized. When, however, current flows thru the resistor 69 in the direction of the arrow a negative bias will be applied to the grid of the tube 48 thus decreasing the current flowing in the winding of the relay I!) which will cause this relay to open.

Referring to Figure 1 it is seen that under normal conditions when no radio signal is received by the receiver IS the relay l9 will be closed and the relay l6 open. If a tank or other object approaches the mine H the detonating circuit 14 will be activated causing the relay IE to close. This will complete a circuit from the battery l8 thru the relays I9 and Hi to the detonator l3 which will be detonated causing the firing of the explosive charge [2.

If, however, the tank I! is transmitting a radio signal in a manner described in connection with Figure 2 the receiver l will be operated to cause the relay l9 to be deenergized, as described in connection with Figure 3. This will make the detonating circuit inoperative so that when the tank passes over the mine II and causes the energization of the relay IS the explosive charge will not be fired and the tank will pass safely over the mine. If the batteries of the receiver l5 become run down the relay l9 will become deenergized thus making the detonating circuit inoperative and the mine will become dead.

It is thus seen that a radio controlled mine is provided which will explode by the passage of any tank or other metal object, which is not transmitting a particular type of radio signal, but which will be made dead or inoperative when a tank transmitting the particular type of radio signal passes over it. The triple modulation and various selective circuits reduce the possibility of the enemy finding the correct combination for operating the receiver.

It is to be understood that the system may be so designed that it operates in the opposite sense. That is the radio receiver [5 may be so constructed that normally, in the absence of any radio signal being received by the antenna 42, the relay I9 will be de-energized and its contact open so that the mine is dead. On receipt of the proper signal, however, the relay [9 will be energized and its contact closed so that the mine then becomes alive.

In this way it is possible to have a mine field normally inactive, so that it may be crossed by tanks without danger, On the approach of the enemy, however, the appropriate radio signal is sent out and the relays IQ of all the mines in the field are energized, so that the whole mine field becomes active and any tank passing over a mine will cause its detonation.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction but may be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

l. A mine comprising a detonator, a detonator circuit including a normally closed relay 9, a radio receiver having means to receive radiant energy, means controlled by said receiver in response to received energy to open said relay and thereby render said detonating circuit inoperative, said radio receiver comprising detector and amplifier means to receive, detect and amplify a radio wave modulated by at least three different signals, the frequency difference between any two of said signals being different selector circuits individually selective of the different signals, combining circuits having means to combine and obtain the beat frequencies between two pairs of said signals, a second combining circuit having means to combine said first beat frequencies and derive therefrom a secondary beat frequency, and means actuating said relay in response to energy of said secondary beat frequency.

2. A mine comprising a detonator, a detonator circuit including a normally closed relay l9, a radio receiver having means to receive radiant energy, means controlled by said receiver in response to received energy to open said relay and thereby render said detonating circuit inoperative, said radio receiver comprising detector and amplifier means to receive, detect and amplify a radio wave modulated by at least three different signals, the frequency difference between any two of said signals being different selector circuits individually selective of the different signals, combining circuits having means to combine and obtain the beat frequencies between two pairs of said signals, a second combining circuit having means to combine said first beat frequencies and derive therefrom a secondary beat frequency, a selector circuit selective of said secondary beat frequency, a detector circuit actuated by energy in said last selector circuit, said relay being actuated by said last detector circuit.

3. In combination, a mine having a detonator, a detonator circuit including a normally open relay and a normally closed relay in series, means responsive to the passage of a vehicle to close said normally open relay, an energizing circuit normally maintaining said normally closed relay closed, a radio receiver having an output circuit adapted to de-energize said energizing circuit for opening said last relay, said radio receiver being responsive to a carrier wave modulated by a plurality of different signals, and a vehicle borne transmitter having means to radiate a carrier wave modulated by said signals, whereby when said transmitter is operated even though the mine is approached by a vehicle, said radio receiver is energized to release said last relay and render said detonating circuit inoperative, whereas when said transmitter is inoperative and the mine is approached by a vehicle, said relays are both closed to render said detonating circuit operative.

4. A radio receiver comprising detector and amplifier means to receive, detect and amplify a radio wave modulated by at least three diiferent signals, the frequency difference between any two of said signals being different, selector circuits individually selective of the different signals, combining circuits having means to combine and obtain the beat frequencies between two pairs of said signals, a second combining circuit having means to combine said first beat frequencies and derive therefrom a secondary beat frequency, a selector circuit selective of said secondary beat frequency, a detector circuit actuated by energy in said last selector circuit, and a work circuit actuated by said last detector circuit.

5. A mine having a detonator, and means for operating said detonator including a pair of circuits and radio receiving means, said detonator operating-means requiring for its operation the energization, substantially simultaneously, of said two circuits, one of said circuits being energized by the approach of a moving metallic object, and the other of said circuits being under the control of said radio receiving means.

6. A mine having a detonator, means including a pair of relays, which, upon energization, are

adapted to set 0! said detonator, means adapted to normally maintain one of the said relays energized, additional means operative upon the approach of a moving metallic object to energils the other of said relays, and radio receiving means operative upon receipt of a pre-arrangad signal to de-energize the normally energised relay.

7. A mine having a detonator, means including a pair of relays which, upon energization. are adapted to set oi! said detonator, radio receiving means adapted to energize one of the said relays upon receipt of a pre-arranged signal, and additional means adapted to energize the other of said relays upon the approach of a moving metallic object.

8. A mine having a detonator, and means for operating said detonator including a pair of circuits and radio receiving means, said detonator operating-means requiring for its operation the energization, substantially simultaneously, of said two circuits, one of said circuits being energized by the approach of a moving metallic object, and the other of said circuits being energized upon receipt by said radio receiving means of a prearranged signal.

JOHN HAYS HAMMOND, Jl. 

